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Template structure (JSON/YAML) in AWS - Commands & Configuration

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Introduction
AWS CloudFormation templates let you describe your cloud resources in a file. This file can be in JSON or YAML format. It helps you create and manage AWS resources automatically and consistently.
When you want to create multiple AWS resources together as one unit.
When you need to keep your infrastructure setup in a file for easy updates and sharing.
When you want to automate the setup of your cloud environment without clicking in the console.
When you want to ensure your infrastructure is the same every time you deploy.
When you want to track changes to your cloud setup using version control.
Config File - template.yaml
template.yaml
AWSTemplateFormatVersion: '2010-09-09'
Description: Simple AWS CloudFormation template to create an S3 bucket
Resources:
  MyS3Bucket:
    Type: 'AWS::S3::Bucket'
    Properties:
      BucketName: example-cloudformation-bucket-12345

AWSTemplateFormatVersion: Specifies the template version.

Description: A short explanation of what this template does.

Resources: The AWS resources to create. Here, it creates an S3 bucket named 'example-cloudformation-bucket-12345'.

Commands
This command checks if the CloudFormation template file is valid before creating resources.
Terminal
aws cloudformation validate-template --template-body file://template.yaml
Expected OutputExpected
{ "Parameters": [] }
→
--template-body - Specifies the path to the template file.
This command creates a new CloudFormation stack named 'example-stack' using the template file.
Terminal
aws cloudformation create-stack --stack-name example-stack --template-body file://template.yaml
Expected OutputExpected
{ "StackId": "arn:aws:cloudformation:us-east-1:123456789012:stack/example-stack/abcd1234-5678-90ef-ghij-klmnopqrstuv" }
→
--stack-name - Names the stack to create.
→
--template-body - Specifies the template file to use.
This command shows details about the created stack, including its status and resources.
Terminal
aws cloudformation describe-stacks --stack-name example-stack
Expected OutputExpected
{ "Stacks": [ { "StackName": "example-stack", "StackStatus": "CREATE_COMPLETE", "CreationTime": "2024-06-01T12:00:00.000Z", "StackId": "arn:aws:cloudformation:us-east-1:123456789012:stack/example-stack/abcd1234-5678-90ef-ghij-klmnopqrstuv" } ] }
→
--stack-name - Specifies which stack to describe.
Key Concept

If you remember nothing else from this pattern, remember: AWS CloudFormation templates define your cloud resources in a file so you can create and manage them automatically and consistently.

Common Mistakes
Using incorrect indentation or syntax in the YAML or JSON template.
CloudFormation templates must follow strict syntax rules; otherwise, validation and deployment fail.
Use a YAML or JSON validator and the 'aws cloudformation validate-template' command before deploying.
Not specifying the full path with 'file://' when using the --template-body flag.
AWS CLI expects the template file path to be prefixed with 'file://' to read it correctly.
Always use 'file://' before the local file path, like 'file://template.yaml'.
Trying to create a stack with a name that already exists without updating it.
Stack names must be unique; creating a stack with an existing name causes an error.
Use a new stack name or update the existing stack with 'aws cloudformation update-stack'.
Summary
CloudFormation templates use JSON or YAML files to describe AWS resources.
Validate templates with 'aws cloudformation validate-template' before creating stacks.
Create stacks with 'aws cloudformation create-stack' and check status with 'describe-stacks'.

Practice

(1/5)
1. What is the main purpose of a cloud template written in JSON or YAML?
easy
A. To manually configure cloud resources one by one
B. To write application code for cloud functions
C. To monitor cloud resource usage in real-time
D. To describe and set up cloud resources automatically

Solution

  1. Step 1: Understand what a cloud template does

    A cloud template is a file that describes cloud resources and how to create them automatically.

  2. Step 2: Compare options with this purpose

    Only To describe and set up cloud resources automatically matches this description; others describe different tasks.

  3. Final Answer:

    To describe and set up cloud resources automatically -> Option D

  4. Quick Check:

    Cloud templates automate resource setup = D [OK]
Hint: Templates automate resource setup, not manual or monitoring tasks [OK]
Common Mistakes:
  • Confusing templates with monitoring tools
  • Thinking templates are for writing application code
  • Assuming templates require manual resource setup
2. Which of the following is the correct top-level section name in an AWS CloudFormation JSON template?
easy
A. Resources
B. Scripts
C. Functions
D. Commands

Solution

  1. Step 1: Recall AWS CloudFormation template structure

    The main sections include Parameters, Resources, Outputs, etc. 'Resources' defines the cloud resources.

  2. Step 2: Identify valid section names

    Only 'Resources' is a valid top-level section; others are not used in CloudFormation templates.

  3. Final Answer:

    Resources -> Option A

  4. Quick Check:

    Resources section defines cloud resources = C [OK]
Hint: Remember: Resources section always defines cloud items [OK]
Common Mistakes:
  • Using non-existent sections like Scripts or Commands
  • Confusing function code with template sections
  • Mixing up template sections with programming terms
3. Given this snippet of a CloudFormation JSON template:
{
  "Resources": {
    "MyBucket": {
      "Type": "AWS::S3::Bucket"
    }
  }
}

What resource will this template create?
medium
A. An EC2 virtual server
B. An S3 storage bucket
C. A Lambda function
D. A VPC network

Solution

  1. Step 1: Read the resource type in the template

    The resource type is "AWS::S3::Bucket", which means an S3 storage bucket.

  2. Step 2: Match resource type to options

    Only An S3 storage bucket matches the S3 bucket resource type.

  3. Final Answer:

    An S3 storage bucket -> Option B

  4. Quick Check:

    "AWS::S3::Bucket" means S3 bucket = B [OK]
Hint: Look for "Type" value to identify resource created [OK]
Common Mistakes:
  • Confusing S3 bucket with EC2 or Lambda
  • Ignoring the resource type string
  • Assuming resource names define type
4. You wrote this YAML snippet for a CloudFormation template but it fails to deploy:
Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-12345678
      InstanceType: t2.micro
      SecurityGroups: my-security-group

What is the likely error?
medium
A. InstanceType is invalid for EC2
B. ImageId must be a number, not a string
C. SecurityGroups should be a list, not a single string
D. Resources section name is misspelled

Solution

  1. Step 1: Check the SecurityGroups property format

    SecurityGroups expects a list of strings, but here it is a single string.

  2. Step 2: Validate other properties

    ImageId is a string (correct), InstanceType is valid, Resources is spelled correctly.

  3. Final Answer:

    SecurityGroups should be a list, not a single string -> Option C

  4. Quick Check:

    SecurityGroups needs list format = A [OK]
Hint: Lists must be in brackets or dash format in YAML [OK]
Common Mistakes:
  • Using string instead of list for SecurityGroups
  • Assuming ImageId is numeric
  • Misspelling Resources section
5. You want to create a reusable CloudFormation template that accepts a bucket name as input and outputs the bucket ARN. Which two sections must you include in your JSON template?
hard
A. Parameters and Outputs
B. Resources and Scripts
C. Functions and Parameters
D. Outputs and Commands

Solution

  1. Step 1: Identify input and output sections needed

    To accept input like bucket name, use Parameters. To show output like ARN, use Outputs.

  2. Step 2: Confirm other sections are invalid

    Scripts, Functions, Commands are not valid top-level sections in CloudFormation templates.

  3. Final Answer:

    Parameters and Outputs -> Option A

  4. Quick Check:

    Input = Parameters, Output = Outputs [OK]
Hint: Parameters take inputs; Outputs show results [OK]
Common Mistakes:
  • Using non-existent sections like Scripts or Commands
  • Confusing Resources with input/output sections
  • Forgetting to include Outputs for results
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